JPS6018887B2 - Combustion control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a forced air combustion system that supplies combustion air using a blower, and by keeping the ratio of air amount and fuel, so-called excess air ratio, within a certain range. In addition to ensuring combustion stability, the combustion efficiency is not reduced even when the combustion amount is adjusted.

In particular, the aim is to reduce the pressure loss in the air system of the air and fuel mixing section, thereby making it possible to downsize the blower, thereby making the entire combustion equipment smaller and lighter. In conventional forced air combustion systems, a burner is placed in the blower system and fuel is supplied to it, but there is generally no relationship between the air side and the fuel side. It is true. In these devices, the amount of air blown and the internal pressure of the device change depending on voltage changes and variations in the blower, changes in the resistance of the air supply path, and the strength of the outside air applied to the air supply and exhaust holes, so the excess air ratio changes. could not be held constant. Also,
When changing the combustion amount, switch the number of burners,
Naturally, since the fuel supply pressure is changed, the excess air ratio also changes significantly. For this reason, it is necessary to select a burner that can withstand changes in excess air ratio, which has resulted in the burner itself becoming larger. Furthermore, when the combustion amount is adjusted to a low value, the excess air ratio increases significantly, resulting in a decrease in combustion efficiency. Examples of combustion that control the excess air ratio include combustion apparatuses used for industrial purposes, such as heating furnaces and heat treatment furnaces.

In these devices, a high-pressure blower with a capacity of several hundred or more water columns is used as the blower, and when gas is used as fuel, it is fed falsely from medium-pressure piping or the gas is pressurized using a booster. Naturally, therefore, not only was the device large in size, but it could not be used in general households where low-pressure gas was supplied. The present invention eliminates the above-mentioned conventional drawbacks, and embodiments thereof will be described below with reference to the accompanying drawings.

In Fig. 1, reference numeral 1 designates a blower for supplying combustion air unevenly, and an injector 2 is disposed in the air system path 4, where fuel and air are mixed and supplied to a premix combustion burner 3 for combustion. . On the other hand, fuel is controlled by a pressure regulator 5, passes through a solenoid valve 6, passes through a fuel supply line 7, and then flows to an injector 2.
supplied to The injector 2 passes from an inlet part 8 located on the upstream side of the air to a constriction part 9 where the diameter is reduced, and then to a constriction part 10.
and an enlarged part 11 which passes through this and whose diameter gradually increases, and these parts are arranged on the same axis. Also, the aperture part 1
There is a fuel injection port 12 facing the inlet end face of the fuel injection valve 0 and provided at the same position D as the constriction portion 10, and is connected to the fuel supply line 7 described above. In this way, fuel is ejected from the center and air is ejected from the periphery of the constricted part 1, and these flow while mixing, and the mixing is promoted in the enlarged part, and the pressure is restored. . 13 is a nozzle for setting the fuel injection amount.

Next, looking at the fuel supply side, the inlet 1 of the pressure regulator 5
Fuel enters from 4, passes through a control valve composed of a valve port 15 and a valve body 16, and flows into a valve chamber 17.

Next, it passes through the differential pressure generating body 18 and is connected to the solenoid valve 6 from the outlet 19. 20 is a main diaphragm for moving the valve body 16, one of which is provided with a diaphragm chamber 22 in which the fuel pressure of the low pressure part 21 of the differential pressure generator 18 is released, and the other is provided with the diaphragm chamber 22 in which the fuel pressure of the low pressure part 21 of the differential pressure generator 18 is released, and the other part is provided with the diaphragm chamber 22 in which the fuel pressure of the low pressure part 21 of the differential pressure generator 18 is released. A back pressure chamber 23 to which air pressure is introduced by a pressure equalization pipe 28 is configured.

Further, 24 is a balance diaphragm having an effective width approximately equal to that of valve 15 and separating the fuel inlet 14 and the diaphragm chamber 22. 25 is an adjustment spring supported by an adjustment screw 26 and acting against the main diaphragm 20.

27 is a blind cap for preventing airtight leakage from the adjustment screw 26.

The operation of the combustion control device having the above configuration will be described next.

In FIG. 1, the air necessary for combustion is sent from the blower 1, and the fuel whose pressure is regulated by the pressure regulator 5 according to the amount of air is released from the fuel jet port 12 of the injector 2 when the on-off valve 6 is opened. It is ejected, mixed with air, and sent to the premix combustion burner 3, where it is combusted.

In this case, the ratio of fuel and air amount is set to an excess air ratio that achieves complete combustion in the burner and the highest thermal efficiency, and input control is performed by changing the air flow, but at that time, the optimal excess air ratio is also set. It is something that is kept. Conventional control mechanisms of this type maintain a constant ratio of air and fuel, and the supply pressure for both is over several hundred water columns, so it was only used for industrial applications where pressure loss at the injector 2 was not a problem. .
In ordinary households, it has been considered impossible to control the excess air ratio because it has not been possible to obtain such high pressure. The present invention improves this point and makes it applicable to household appliances. First, Figure 2 is an enlarged cross-sectional view of the injector 2. The pressure in section 10 decreases.
The pressure difference between the inlet section 8 and the constriction section 10 is determined by the air velocity passing through the annular air passage defined by the fuel injection row 2 and the constriction section 10 at the inlet of the constriction section, as shown in Fig. 3. become. If expressed in a mathematical formula, Pai-Pn=ka(
VC)2=Ka(QC)2--E)Pa
i: Pressure Pn at the inlet section 8: Pressure Vc at the constriction section 10: Air ejection speed Qc: Air amount Ka is a constant determined by the size and shape of the striped flow section 9 and the constriction section 10.

The pressure Pn of the throttle section 10 given here is not the pressure acting on the wall surface of the throttle section 10, but is the effective pressure acting on the fuel jet port 12 facing the end of the throttle inlet. Next, regarding the pressure regulator 5, the fuel flow rate is determined by the pressure at its outlet 19 and the aforementioned throttle pressure Pn.

The relationship is as shown in the following equation '2). Qg=KgノP
go-pn... ■QZ: Fuel flow rate P battle: Pressure at the outlet 19 of the pressure regulator 5. Kg is the pressure at the on-off valve 6 or nozzle 13 in the fuel supply line 7.
It is a constant determined by the dimensions and shape of the fuel and the specific weight of the fuel.

In combustion burners, the excess air ratio, which is expressed as the ratio of the air amount to the theoretical air amount of the fuel, is a problem, and the relationship is as follows.

M = for. ...【3' M: excess air ratio q: Theoretical air amount per unit fuel flow rate Substituting the ‘1’ and ■ expressions into the ‘3’ expression, we get J ai-Pn) M=volume-q・KMg.

-pn-q-Kg≧Jha-”Poisonous sweet potato spicy =K5 key word skewer ---■ ・ However, K=q. Ka. It is a.

Here, it is assumed that the relationship between the pressure Pgo at the outlet 19 of the pressure regulator 5 and the pressure Pai at the inlet 8 of the injector 2 is expressed by the following equation.

Pgo = Pai ten △P
...[51 This shows that there is a difference of △P between P arc and Pai, and by substituting this '5} formula into formula [4], we get M = K - Pn = /P sheep insect PPqo-P
n = to/1 ten-tone student Pn (6) '61 formula is obtained.

Therefore, if the outlet pressure Pqo on the fuel side and the inlet pressure Pai on the air side become equal so that ΔP becomes zero, the excess air ratio is determined only by the dimensions and shape that can be set in advance, regardless of the flow rate. The pressure regulator 5 controls the relationship of the control valve so that ΔP shown in equation (2) becomes zero. Since the pressure on the fuel side and the pressure at the injector inlet section 8 act on the main diaphragm 20, for example, if the pressure on the fuel side becomes high, the valve body 16
The diaphragm moves in the direction of closing the valve body 16, and conversely, when the pressure on the air side increases, the diaphragm moves in the direction of opening the valve body 16, both of which act in the direction of eliminating the pressure difference. Incidentally, it is not possible to completely reduce ΔP in equation [5' to zero, but the influence thereof will be described in FIGS. 4 and 5. Figure 4 shows [△P (=P paddy - Pai) in formula 5'
Let the standard excess air ratio when is zero be M, and its plus
△P and the effective pressure difference (Pai
-Pn).

This is as shown in equation '6', and as the generated pressure difference increases, the value of ΔP that causes the same fluctuation in excess air ratio increases. Conversely, if the value of ΔP is the same, the smaller the generated pressure difference, the more likely the value of the excess air ratio will fluctuate. FIG. 5 shows the relationship in another representation. Pqo-Pai (i.e. △P
) How far is the excess air ratio M from the standard state?
This shows how things change. Here, the cause of ΔP will be described. This means considering the difference between the air pressure in the back pressure chamber 23 of the pressure regulator 5 and the fuel pressure at the outlet 19. First, in the case of gas, the fuel supply pressure is different for city gas, natural gas, and LP gas, and the pressure drop in the piping differs when gas demand is concentrated and when demand is small. Therefore, the actual supply pressure is said to vary by more than six times, including the difference in gas quality.

As shown in FIG. 1, a balance diaphragm having an effective width approximately equal to that of the valve port 15 is used to balance the force trying to open the valve body 16 and the force generated by the balance diaphragm and trying to close the valve body 16. Methods are used to eliminate or, in practice, completely balance the effect of supply pressure. This is because, for example, even if the combustion input is the same, the gas flow rate is 5 to 6 times different between city gas and LP gas.
6 have different degrees of closure. As a result, balance diaphragm 2
This is because the operating position of 4 is changing, and its effective diameter is also different. When gas is supplied at a preset gas pressure, as in the case of industrial use, this effect does not need to be considered. The next factor is the influence of flow rate changes. This is possible when the input is varied for the purpose of temperature control with the same combustion device, or when the flow rate changes depending on the gas quality even with the same input.
If it were to be controlled up to /3, the flow rate would change by a factor of 15 to 18, including the difference in gas costs. It is generally known that in a gas pressure regulator, the outlet pressure decreases as the flow rate increases. This is due to an increase in pressure loss inside the regulator as the flow rate increases, a change in the effective diameter of the main diaphragm due to the movement of the valve body in the opening direction, and a change in the spring load. For example, as shown in Figure 6. It will look like the A line. That is, even if the pressure is regulated at a certain point, the outlet pressure decreases as the flow rate increases. The pressure regulator 5 shown in FIG. 1 is designed to improve this tendency and reduce the above-mentioned ΔP. The pressure in the diaphragm chamber 22 is not the pressure at the outlet 19, but the pressure at the low pressure section 21 of the differential pressure generator 18 is applied. In Fig. 6, the difference between the back pressure chamber 23 and the back pressure chamber 23 is shown as a reference. be. By applying a pressure lower than the outlet pressure C to the diaphragm chamber by the reed pressure generator 18, the pressure in the valve chamber 17 is increased. As for the differential pressure generator itself 18, the pressure drop is represented by B-C, and the differential pressure between the low pressure part 21 and the outlet 19 is represented by C-A. In either case, there are approximately two relationships with respect to the flow rate, so if line A is used as a reference, the relationship will be as shown in the same figure. When the flow rate increases, the valve body 16 opens and the outlet pressure decreases for the reasons mentioned above, but this is compensated for by applying a pressure even lower than the outlet pressure to the diaphragm. The degree of this compensation is determined by the characteristics of the differential pressure generator, and the characteristics shown in lines A to 2 in FIG. 7 can be arbitrarily selected depending on the specifications of the low pressure section 21. When performing such compensation, it is most suitable for the combustion control device of the present invention to perform it as follows. As explained in Fig. 4, the problem is most when the pressure difference generated at the injector 2 is small, but this is because the amount of combustion air is small.
Therefore, this applies only when the flow rate of fuel supply is small.
Therefore, ΔP should be minimized at the flow rate that corresponds to the minimum input. For general household use where gas quality cannot be determined, a differential pressure generator is used to compensate for the change in outlet pressure due to the change in flow rate between the LP gas flow rate corresponding to the minimum input and the city gas flow rate. It is good to set it up. According to experiments, the value of ΔP was as follows. However, the input variable width is up to 1/3. According to this experiment, not only △P itself has decreased, but also △P due to flow rate changes.
There are also fewer changes. The result of 8.25 is preferable due to the influence of flow rate changes due to gas quality at the lowest input, but
In this case, since the pressure loss as the pressure regulator 5 is increasing, △P will increase when the supply pressure decreases, so for home use, the factors that cause △P mentioned above should be considered. Must be considered comprehensively. In addition to the above, △P
The causes of this include variations in pressure regulation by the adjustment screw 26 during manufacture and changes in diaphragm rigidity due to temperature. The factors of △P shown in equation (■) have been described above, but as mentioned above, as for the pressure regulator 5, the excess air ratio fluctuates within the range shown in Fig. 5. The pressure difference Pai-P caused by the injector depending on the amount
If n is 5 water columns and the allowable range of excess air ratio M is from 120% to -20% depending on the burner conditions, then
The value of ΔP must be controlled to fall between -1.8 and 12.81 water columns.

This value must be maintained despite all external variables and manufacturing variations. Here, even if the pressure difference of the injector 2 is the same and the amount of air is the same, if a larger amount can be obtained, ΔP may be larger, but there are restrictions in this respect as well.

This is because, in order to increase the pressure difference Pai-Pn, the pressure loss of the injector 2 increases, which not only increases the size of the blower, but also increases the absolute value of Pai. However, there is a limit to the V supply pressure in domestic gas piping, and in particular for city gas, it is said that it may drop to 5 volts of water column. Furthermore, when the air supply and exhaust pipes are exposed to the outside air, if the wind blows at 2 blood per second, the internal pressure will increase by 15 to 2 mw water columns.
This increase in internal pressure means that the absolute value of Pai increases, so if we look at it as ΔP expressed as P and Paj, it means that the supply gas pressure has decreased by 15 to 2 columns of water. As a result, even if the valve body 16 of the pressure regulator 5 is fully opened, P
go<Pai, resulting in an increase in excess air ratio due to insufficient gas amount. Therefore, unless gas is supplied from a booster or medium-pressure gas piping, as in industrial use, ΔP cannot be reduced to zero even if a large blower is used. For household use, the effective pressure difference Pai - Pn can be reduced without increasing the pressure Pai at the inlet 8 of the injector 2.
It is important to obtain a large amount of , and this is a major point of the present invention. The injector 2 has a configuration as shown in Fig. 2. First, the direction in which air is ejected and the direction in which fuel such as gas is ejected are the same and the vectors match, so disturbances due to interference between the two fluids are less likely to occur and kinetic energy loss is reduced. Or, compared to a Venturi mixer seen in industrial use, where the direction of air and the direction of gas ejection are at right angles, there is less ejection.

This is advantageous when mixing is performed at a portion where pressure loss is likely to occur, such as the constriction section 10. Next, assuming that the inner diameter D of the throttle part 10 is constant, its length t, and the outer diameter d of the fuel injection port are
This section describes the relationship between the pressure drop and the pressure drop.

Note that here, the pressure loss is a value expressed by the following formula. P
Les OSS=Paj-Pao
...[71Pao: Air pressure at the part exiting the enlarged part 11 PLOSS: Pressure loss at the injector 2 In Fig. 8, the amount of air continues to flow at a certain amount and the gas from the fuel jet port 12 gradually increases from zero. It shows the relationship of pressure loss when

When there is no gas ejection, the pressure loss is small (within the experimental range, when the gas ejection speed is slow compared to the air ejection speed, the pressure loss tends to increase as the gas amount increases). When d/D is large, the air ejection area is small, so the pressure loss itself is large, but the change depending on the gas amount is also large. Moreover, not only does the pressure loss change depending on the t/D, but also the tendency of change depending on the gas amount. Next, consider the pressure efficiency valve hole opening degree of the injector 2. ai-Pn)-
P.L.

ssri = Paj-Pn Pao-Pn ・
・The higher the efficiency of this sword, the better it is.

According to experiments, the results shown in Figure 9 were obtained. In other words, the smaller d/D is, the higher the efficiency is, and the point of maximum efficiency with respect to t/D becomes smaller as d/D becomes larger.
D is also moving to a large value. Figure 9 shows the actual effective Pa
-Pn is determined, a pressure efficiency curve is calculated from the pressure loss at that time, and the point with the lowest efficiency is plotted to create the pressure efficiency curve. Here, it is advantageous to set d/○ small because the pressure efficiency is high and t/D can be reduced, but for home use, Pai cannot be made too high for the reasons mentioned above, so Pgo is also low. In order to allow the fuel to flow, there is a restriction that d cannot be made too thin. Furthermore,
In FIG. 10, the concentration distribution of air and gas at the exit surface after passing through the enlarged part 11 of the injector 2 is obtained.
This uses d/D at t/D as a parameter. The results show that the larger d/D is, the more uniform the concentration distribution is. It is desired that the excess air ratio of the burner 3 as a whole is within a predetermined range, and that the excess air ratio of each flame hole alone is also controlled. Injector 2 and burner 3
It goes without saying that it is preferable to promote uniformity of the concentration distribution in the injector 2 itself. According to these experimental results, the t/D is 0.5~
3 and d/D of 0.3 to 0.5 was found to be best from the viewpoint of pressure efficiency and concentration distribution. Next, the positional relationship between the tip of the fuel jet 012 and the throttle part 10 will be explained. When the alignment with the inlet end face of the constricted portion 10 is indicated by 〆n as shown in Fig. 2, the pressure loss and the generated pressure difference were obtained as shown in Fig. 11. That is, the generated pressure difference tends to decrease as it moves away from the inlet end face, and rapidly decreases when it moves away from it by more than 25% of the inner diameter D of the constriction part. Further, when the air is introduced into the constricted portion 10 from the inlet end face, the ejection area of the air remains unchanged, so the generated pressure difference does not decrease, but rather increases by the amount of friction. However, pressure efficiency decreases. Therefore, the position where a generated pressure difference above a certain level can be obtained and the pressure efficiency is high is to position the tip of the fuel nozzle 12 within 0.2 degrees of the aperture diameter back and forth around the inlet end face. We obtained good results. Furthermore, regarding the enlarged portion 11, as is generally known, the pressure loss is minimized when the enlarged angle is around 8 degrees. The injector 2 is configured with each of the above elements, and it is now possible to obtain a large generated pressure difference with less pressure loss.
It has become possible to obtain a device that can sufficiently control the excess air ratio even at low gas pressures.

In the case of gas, the fuel flow rate differs even with the same input, but in that case, it is sufficient to change the constant X9 shown in equation {21. Specifically, only the nozzle 13 shown in FIG. 1 is replaced. The pressure regulator 5 itself and the injector 2 may be left as they are even if the gas quality changes. If an on-off valve is inserted on the fuel side to turn on and off the input as necessary, it is preferable to insert it between the pressure regulator 5 and the injector 2 as shown in FIG. This is because, as already explained, if we consider the case where the gas supply pressure in the home decreases, in order to keep △P at zero, it is necessary to enter the pressure regulator 5 with a supply pressure higher than Pai. Therefore, the pressure loss upstream of the pressure regulator 5 must be minimized as much as possible. Since the solenoid valve provides pressure loss from the water column on the few side to the water column on the tenth side, considering this as a factor of the constant kg shown in equation 21, it is better to do as shown in Figure 1 to reduce the air pressure loss against the drop in gas pressure. Changes in excess rate can be reduced. For example, if we assume that the pressure loss of a solenoid valve is the IW water column, and consider what will happen to the gas pressure that will cause the excess air ratio to increase by 20% compared to the air excess ratio when the gas pressure is 10 m. If it is placed upstream of 5 and the water column is 6, then the arrangement shown in Figure 1 can withstand a drop in gas pressure up to 5Q. According to the control device of the present invention, since the fuel flow rate is controlled according to the amount of combustion air, input control is possible only by controlling the amount of air from the blower 1. For general household use, it is necessary to control the input according to the load from the standpoint of usability and energy saving, and in that respect it can be said that the device is easy to control. In FIG. 1, all air is supplied as primary air, but if secondary air is required, it may be branched from the air supply line 4 and supplied directly to the burner 3.

Even at that time, the ratio of primary air to secondary air can be set in advance, so the ratio of primary air, secondary air, and fuel flow rates can always be kept constant.

As described above, according to the present invention, the excess air ratio is not only kept almost constant even when there are changes in the input, fuel supply negative pressure, outside air wind pressure, etc., and complete combustion is possible, but also when the input is low. It also does not cause a decrease in efficiency.

In particular, by increasing the pressure efficiency in the mixing section of air and fuel, it is possible to use the blower at low pressure, which not only makes the blower more compact, but also makes it suitable for general household use.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view of an injector, FIG. 3 is a diagram showing the relationship between air velocity and generated pressure difference in the injector, and FIGS. The figure shows the difference in generated pressure and the influence of the pressure regulator on the change in excess air ratio due to the sex hall. Figures 6 and 7 are diagrams explaining the relationship between the outlet pressure fluctuation and the flow rate of the pressure regulator. 8,9,10,
FIG. 11 is a diagram showing the influence of various elements of the injector. 2...Injector, 3...Premix combustion burner, 4...
...Primary air system path, 5...Pressure regulator, 6...
...Opening/closing valve, 7...Fuel supply line, 8...
...Inlet chamber, 10... Throttle part, 11 Enlarged part, 12... Fuel spout, 13... Nozzle,
15... Valve hole, 16... Valve body, 18...
... Differential pressure generator, 20 ... Main diaphragm, 21 ... Low pressure section, 22 ... Diaphragm chamber, 23 ... Back pressure chamber , 24...
Balance diaphragm, 28... pressure equalization tube. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (1)

[Scope of Claims] 1. A premix combustion burner that requires primary air, a primary air system passage for supplying primary air, and a premix combustion burner that is provided in the primary air system passage and has substantially the same diameter and 0.5 to 3 of the inner diameter thereof. A constriction part with twice the length, an enlarged part that communicates with the constriction part and enlarged until it becomes equal to the burner inlet diameter, and a concentric constriction with the constriction part that has an outer diameter of 0.3 to 0.5 times the inner diameter of the constriction part. an injector having a fuel spout located at the end face of the inlet; a fuel supply line communicating with the fuel spout; a valve body provided in the fuel supply line for controlling the opening degree of the valve hole; A differential pressure generator consisting of a ventilated tube-shaped constriction section, a low pressure section, and an expansion section, a balance diaphragm having an area approximately equal to the valve hole on the opposite side of the valve hole, and a main diaphragm having an area larger than the balance diaphragm. a pressure regulator which connects both diaphragms and a valve body and communicates the diaphragm chamber formed between the two diaphragms with the low pressure part of the differential pressure generator, and the inlet chamber of the injector and the main diaphragm of the pressure regulator. A combustion control device consisting of a pressure equalizing pipe that communicates with a back pressure chamber formed on the opposite side of the valve body, and a nozzle installed in the fuel supply line between the pressure regulator and the fuel injection port. 2. The combustion control device according to claim 1, wherein the combustion control on-off valve is disposed in the fuel supply line between the fuel injection port and the pressure regulator.